A crate exists that solves this particular problem. Using the example given by @paholg:

use std::ops::Deref;

use disjoint_impls::disjoint_impls;

disjoint_impls! {
    trait Foo {}

    impl<T> Foo for T where T: Deref<Target = u8> {}
    impl<T> Foo for T where T: Deref<Target = bool> {}
}

fn main() {}